1. Field of the Invention
The present invention generally relates to a self-aligning cutter hub assembly mounted on the end of the drive shaft of an underwater pelletizer which orients the cutter hub and blades mounted thereon in optimum aligned relation to the die face of the extrusion die plate of the underwater pelletizer. More specifically, the present invention represents an improvement on the self-aligning cutter hub structure disclosed in U.S. Pat. No. 5,624,688 (owned by the Assignee of the present application) and includes an assembly retainer in the form of spring pins or attachments to retain the self-aligning cutter hub elements within the bore of the cutter hub when the underwater pelletizer is disassembled.
2. Description of the Prior Art
Underwater pelletizers for forming plastic pellets by the use of an extrusion die having orifices through which molten polymer is extruded out from a die face for engagement by cutter blades mounted on a rotatable cutter hub and driven by a drive shaft are well known. One of the characteristics of underwater pelletizers is the desirability of maintaining the cutter blades and die face in properly aligned relation in order that the cutting edge of the blades on the rotating cutter hub move in very close parallel relation to the die face. This close parallel relationship allows the blades to efficiently cut the extruded plastic into pellets as the plastic strings are discharged from the orifices in the extrusion die plate and prevents unnecessary wear of the cutter blade and/or die plate face. The following additional U.S. patents, also owned by the Assignee of this application, relate to underwater pelletizers, cutter hub assemblies and structures for positioning the cutters and cutter hub in desired relation to the die face of the die plate:
The above referenced patents, and the references cited in those patents, which are incorporated herein as if fully identified, disclose various underwater pelletizer structures and components thereof.
With respect to U.S. Pat. No. 5,624,688 this patent discloses a self-aligning cutter hub assembly which connects the cutter hub to the pelletizer drive shaft. The assembly transmits torque from the drove shaft to the cutter hub while at the same time allowing limited universal movement of the cutter hub in relation to the rotational axis of the drive shaft. This universal movement enables the cutter blades on the cutter hub to maintain optimum parallel relation to the die face of the extrusion die plate to efficiently cut the extruded plastic material into pellets. The structure connecting the cutter hub to the drive shaft also enables effective assembly and disassembly of the components of the cutter hub onto and off of the end of the drive shaft.
More specifically, the cutter hub of the ""688 patent includes a central bore defining an inner surface and an adapter received in the bore and fixedly attached to the end of the drive shaft. The inner surface of the hub bore and the outer surface of the drive shaft adapter are provided with corresponding partial spherical surfaces which coact to enable the requisite universal movement of the cutter hub in relation to the drive shaft. The drive shaft adapter is mounted on the end of the drive shaft, as by screw threads or the like, and the adapter and hub bore each include diametrically arranged recesses for partially receiving spherical balls which transmit the driving torque from the drive shaft to the cutter hub.
The recesses on the inner surface of the cutter hub bore are preferably diametrically opposed axial recesses or grooves which extend inwardly from one end surface of the cutter hub but do not extend completely to the other end surface of the cutter hub. The inner surface of the cutter hub bore also includes a short circumferential recess extending from each edge of the axial recess or groove and opening to the end surface of the cutter hub open to the axial recess. The recesses enable the adapter and torque transmitting balls to be assembled into the bore of the cutter hub when the adapter is oriented in perpendicular relation to the surface of the cutter hub. The drive shaft adapter can then be rotated 90xc2x0 to register the partially spherical inner surface in the bore of the cutter hub with the partial spherical outer surface of the adapter.
The recesses or grooves in the inner surface of the cutter hub bore receive the torque transmitting balls during assembly of the drive shaft adapter with pivoting of the adapter into final position locking the torque transmitting balls in position. The adapter can then be assembled onto the drive shaft, such as by a screw threaded engagement between the drive shaft and adapter or other engagement assembly.
When handling the self-aligning cutter hub assembly as disclosed in the ""688 patent, either when assembling for installation in the pelletizer or when disassembling to change or adjust components of the pelletizer, in some instances, the drive shaft adapter can pivot to a position perpendicular to the cutter hub. In this position, the adapter can fall out of or disassemble from the hub by gravity if the hub is supported with the open ends of the axial recesses facing downwardly or when a force is applied to the adapter that would move the balls out of the axial recesses or grooves in the hub. When this occurs, the torque transmitting balls may fall out of the recesses in the adapter and become lost or require considerable time and effort to locate. Then additional time is required to reassemble the balls, adapter and cutter hub.
In order to overcome the foregoing difficulty, the present invention provides an assembly retainer for the cutter hub which includes a structure that places an obstruction in the open end area of the axial recesses. This obstruction then prevents the torque transmitting balls from moving out of the axial recesses thereby maintaining the hub, drive shaft adapter and balls in assembled relation when the self-aligning cutter hub is not assembled on the drive shaft such as when components of the cutter hub are being replaced, adjusted and the like.
In one embodiment, the assembly retainer for the self-aligning cutter hub includes a circular plate or washer associated with the open end of each axial recess in which a torque transmitting ball is positioned to prevent the ball from exiting the open end of the axial recess. The ball retaining plates or washers are secured to the cutter hub by the use of a screw threaded fastener or the like extending into the end surface of the cutter hub to which the axial recess opens, thereby retaining the adapter, balls and cutter hub in assembled relation and preventing accidental disassembly when the cutter hub is being handled, attached to the drive shaft, detached therefrom or otherwise not associated with a die plate or drive shaft.
In a second embodiment, the assembly retainer for the self-aligning cutter hub includes spring pins inserted in angular passageways in the cutter hub which communicate with the open end of the axial recesses in the bore of the cutter hub. A spring pin is inserted in each of the angular passageways with one end of each spring pin terminating in the end of the axial recess and forming an obstruction to prevent the torque transmitting balls from exiting the axial recesses in the cutter hub and limiting the pivotal movement of the cutter hub in relation to the adapter during assembly, disassembly and adjustment of the cutter hub.
Preferably, the cutter hub and drive shaft adapter are each provided with four recess arrangements oriented at 90xc2x0 positions around their circumference. Having four recess arrangements facilitates maintenance and enhances the life of the self-aligning cutter hub by enabling an operator of the pelletizer to initially use one set of the diametrically opposed recesses in the outer surface of the adapter, one pair of balls and one set of recesses in the inner surface of the bore together with appropriate retainers. Then, after requisite use and wear, the pelletizer operator may remove the assembly retainer, disassemble the adapter and balls from the hub and then reassemble the adapter, balls and hub utilizing the previously unused set of diametrically opposed recesses in the adapter and hub and inserting the retainers in the same manner as when oriented in relation to the originally used recesses. Optionally, a new set of balls may also be used if the original balls show any evidence of wear. As such, the present invention enables a prolonged useful life of the self-aligned cutter hub which will be retained in assembled relation by the assembly retainers during handling, assembly, disassembly and adjustment of the cutter hub assembly.
Accordingly, it is an object of the present invention to provide a self-aligning cutter hub assembly which includes an assembly retainer to keep the torque transmitting balls from coming out of the cutter hub axial recesses when the components of the cutter hub are being replaced, adjusted and the like.
Another object of the present invention is to provide a self-aligning cutter hub with an assembly retainer which keeps the drive shaft adapter from inadvertently disassembling from out of the cutter hub bore during handling, assembly, disassembly and adjustment of the cutter hub assembly.
A further object of the present invention is to provide a self-aligning cutter hub assembly with an assembly retainer which keeps the cutter hub from coming apart when the hub is handled improperly during replacement, adjustment, etc. of the pelletizer components.
Still another object of the present invention is to provide a self-aligning cutter hub assembly which has a prolonged useful life by reason of a duplicate pair of diametrically opposed recesses in the cutter hub and drive shaft adapter, thus providing duplicate assembly arrangements.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.